In a machine used to raise water for the purpose of irrigation, as described by Vitruvius
(X.4),º the vents through which the water was conveyed into the receiving trough, were termed Columbaria. This will be understood by referring to
the woodcut at p100 [Antlia]. The difference between that representation and the machine now under consideration, consisted in the following points:— The wheel of the latter is a solid one (tympanum), instead of radiated (rota); and was worked as a treadmill, by men who stood upon platforms projecting from the flat sides, instead of being turned by a stream. Between the intervals of each platform a series of grooves or channels (columbaria) were formed in the sides of the tympanum, through which the water taken up by a number of scoops placed on the outer margin of the wheel, like the jars in the cut referred to, was conducted into a wooden trough below (labrum ligneum suppositum, Vitruv. l.c.).

The cavities which receive the extreme ends of the beams upon which a roof is supported (tignorum cubilia), and which are represented by triglyphs in the Doric order, were termed Columbaria by the Roman architects; that is, whilst they remained empty, and until filled up by the head of the beam.a The corresponding Greek term was ὀραί (from ὀπή, a hole), and hence the space between two such cavities, that is, in the complete building, between two triglyphs, was called μετόπη, a metope
(Vitruv. IV.2; Marquez, Dell' Ordine Dorico, VII.37).